Conventional manufacture processes of solid oxide fuel cells (SOFCs) include the provision of a metallic support, the formation of an anode layer thereon followed by the application of an electrolyte layer. The so formed half cell is dried and afterwards sintered often in a reducing atmosphere. Finally, a cathode layer is formed thereon so as to obtain a complete cell. However, during the sintering of the half cell undesired reactions between the metal support and anode materials occur resulting in a negative impact on the overall cell performance.
WO-A2-2005/122300 relates to a solid oxide fuel cell with the anode on the metal support side comprising a metallic support ending in a substantially pure electron conducting oxide that prevents the reaction of metals of the anode with said metallic support, which is normally a ferritic stainless steel. The complete cell contains on top of the metallic support, an active anode layer, an electrolyte layer, an active cathode layer and a transition layer to a cathode current collector of a single phase LSM. A discrete barrier layer is provided between the electrolyte layer and the cathode layer in order to increase the lifetime of the cathode layer by preventing the diffusion of cations from the cathode layer into the electrolyte layer.
WO-A2-2006/082057 discloses a fuel cell in which the cathode layer is provided on a metallic support normally a ferritic stainless steel support enabling thereby the provision of robust cell which at the same time eliminates the problem of deterioration of the metallic support otherwise encountered in designs, where the anode layer is provided on the metal support side. By having the cathode layer on a metallic support the reactions of active anode components such as Ni with the ferritic steel of the support are avoided. A discrete barrier layer of doped ceria is provided in between the electrolyte and the cathode layer to prevent the diffusion of cations from the cathode to the electrolyte. The provision of the cathode on the metallic support side enables a more robust cell. The degrees of freedom in choice of anode material are increased and at the same time redox stability is enhanced. However, corrosion of the metallic support may still take place and severely impair the applicability of this otherwise attractive cell design. Moreover, at the operating temperatures of SOFC often between 700° C. and 900° C., chromium present in the metallic support, which is normally ferritic stainless steel, has a strong tendency to migrate into the cathode and severely impair the performance of the cell by significantly decreasing the power density due to degradation of the cell. This phenomenon is known in the art as Cr-poisoning.
D. E. Alman et al. Journal of Power Sources 168 (2007) 351-355 describe the preparation of a fuel cell in which a thin and dense metal sheet of ferritic stainless steel is perforated to form a current collector with a slotted pattern which allows the passage of air to the cathode. The perforated metal sheet is then coated with ceria and subsequently attached to the anode or cathode side of a button cell. The button cells contain a thin Gd-doped ceria layer at the electrolyte-cathode interface. The provision of a ceria coating on the metal surface (as a thin oxide layer) reduces cell degradation due to Cr poisoning. However, only the outer surface of the metal is covered with the ceria.
It would be desirable to be able to provide solid oxide cells which are robust and with higher corrosion stability and higher resistance against Cr-poisoning than prior art cells.